The new iMac has a bunch of changes, the first is the design. For the first time since 2009, the iMac has been redesigned and takes up 40% less volume, and has a screen with 75% less glare. This makes a huge difference.
In terms of the internals, the processors are current generation, 2012 'Ivy Bridge' chips, which are much faster even at the same clock speeds. It's not hugely noticable over the 2011 models, but if your computer is older, you'll notice a huge jump. 8GB of RAM now comes as standard, but is configurable to 16GB in the 21.5 inch model, and user upgradable in the 27 inch.
There are a couple of compromises, for example, there is no disk drive, and the hard drive in the 21.5 inch model spins slightly slower, but not too noticably.
If you're toying between an old or new model, then do go for the new one, it's worth the investment. Below are a couple of reviews from trusted sources:
Let me know if you have any more troubles,
Other than the usual spec bump, such as better processor, the main difference is that the optical drive is removed, which contributed to the overall slimmness. There are now two microphones, which provides better noice cancellation. For the 21.5 inch model, you cannot easily upgrade the RAM as there is no removable slot at the back. However, for the 27 inch model, you can easily upgrade the RAM.
When you buy the iMac, you also have the option to configure it with Fusion drive. It is basically a combination of an SSD and a hard drive bundled together so that you get the data access speed of SSD and more disk space of the hard drive. The software will cleverly move files around on either SSD or hard drive for you depending on how frequent you use your files or applications.
Jeff Nitschke wrote:
USB 3 would also be a notable mention.
Strange that I totally forgot that--getting old, I guess. USB3 is one of the reasons I decided to update my mid-2010 27".
Not to mention no FW800 ports, just Thunderbolt. For FW800 you need a $29 adapter.
Of course there's always the fact that I never have to worry ever again about putting my SD cards into my CD slot--I consider that to be a major plus.